The present invention relates to an improved fuel cell and, more particularly, this invention relates to a single membrane, hollow fiber liquid fuel/oxygen fuel cell.
In view of current and future domestic energy shortages there is a critical need for more efficient systems for conversion of chemical energy to electrical energy. Electrical energy is the only form of energy that is readily produced, transported, can be utilized in a controlled manner, and can be transformed to other forms of energy at nearly 100% efficiency.
The conventional methods, apart from hydroelectric power generation, of converting primary forms of energy, i.e. solar, chemical, nuclear and gravitational, to electricity pass through an intermediate conversion stage of heat energy to mechanical energy. Inherent losses occur due to the Carnot limitation and moving parts are subject to frictional losses and mechanical failure.
Direct methods of conversion are preferred due to simplicity, reliability, higher conversion efficiency and less weight and volume required by these systems. Thermoelectric, thermionic, photovoltaic and magnetohydrodynamic methods are not finding large scale application due to limitations of materials and energy/unit ratios are small.
The most promising method of direct conversion of primary sources of energy to electricity is the electrochemical method as embodied in the gaseous fuel cell such as the hydrogen-oxygen fuel cells utilized in recent space probes. Fuel cells use extremely complex flat stack arrangements consisting of a membrane, gaskets, channels, electrodes and current collectors that are difficult and expensive to fabricate, and, in the case of solid polymer electrolytes, are subject to catastrophic failure of the total system if there is one pinhole leak in the membrane between the oxygen and hydrogen sides. There is the example of a hollow fiber configuration for a single membrane fuel cell by Brown and Levine in U.S. Pat. No. 3,228,797. However, only very low power densities are obtained in this case because of high internal resistance and inefficient electrode and current collector configuration. Furthermore, this configuration would also fail if any membrane leakage took place.
In their theoretical treatment entitled "Fuel Cells-Their Electrochemistry," Bockris and Srinivason mention a dual spaghetti-tube fuel cell concept with electrodes and active fuel cell processes to occur on the outside of the tubes. However, this concept has the serious limitation that operation requires diffusion of hydrogen and oxygen through the membrane walls, and an operating fuel cell of this type has not yet been devised.
In our prior U.S. Pat. No. 4,100,331 issued July 11, 1978, an improved fuel cell is disclosed which comprises a pair of electrodes immersed in aqueous electrolyte, each electrode being formed of an ion-permeable, gas-impermeable hollow fiber having catalytic electrode material deposited on its inner surface and having a large surface area current collector in contact with the catalytic surface. In accordance with our prior patent, fuel gas, such as hydrogen, is flowed through the fuel electrode and an oxidizing gas, such as oxygen, flows through the oxidizer electrode, resulting in an electric potential being developed which can be recovered and utilized or stored through the circuit joining the electrodes.
Although the fuel cell disclosed in our prior patent overcomes a number of problems present in prior fuel cells and is well suited for its intended purpose, it would be desirable to provide a fuel cell which is not dependent on the use of fuel gases, such as hydrogen, which require the use of special pressure tanks and related equipment.